docs: def get_attachment_content(self, ticket_id, attachment_id):
          """ Get content of attachment without headers.
  
          This function is necessary to use for binary attachment,
          as it can contain ``\\n`` chars, which would disrupt parsing
          of message if :py:meth:`~Rt.get_attachment` is used.
  
          Format of message::
  
              RT/3.8.7 200 Ok\n\nStart of the content...End of the content\n\n\n
  
          :param ticket_id: ID of ticket
          :param attachment_id: ID of attachment
  
          Returns: Bytes with content of attachment or None if ticket or
                   attachment does not exist.
          """
  
          msg = self.__request('ticket/{}/attachments/{}/content'.format
                               (str(ticket_id), str(attachment_id)),
                               text_response=False)
          lines = msg.split(b'\n', 3)
          if (len(lines) == 4) and (self.RE_PATTERNS['invalid_attachment_pattern_bytes'].match(lines[2]) or self.RE_PATTERNS['does_not_exist_pattern_bytes'].match(lines[2])):
              return None
          return msg[msg.find(b'\n') + 2:-3]